The purpose of this study is to evaluate whether pressure support settings suggested by the B3 system and pressure support as well as Positive End Expiratory Pressure (PEEP) settings suggested by the B5 system, i.e. balancing under and over support based upon physiological models and simple clinical measures, are consistent with keeping patients within appropriate levels of support as assessed by the ratio between airwaiy pressure generated by the respiratory muscles (Pmus) and the maximum inspiratory pressure (MIP) (Pmus/MIP), the ratio between the inspiratory time (TI) and total respiratory time (TTOT) (TI/TTOT) and the Tension-Time index (TTi), these being obtained using less frequently used esophageal catheter measurements.